How does anal sac adenocarcinoma typically present and what is the standard surgical and adjuvant approach?

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Apocrine gland anal sac adenocarcinoma (AGASACA) most commonly presents with signs of mechanical obstruction from the primary tumor or enlarged regional lymph nodes, with paraneoplastic hypercalcemia — manifesting as polyuria and polydipsia — present in approximately 25% to 50% of cases. 5 AGASACA comprises approximately 17% of perianal malignancies in dogs and 2% of all skin tumors, and it is one of the most common causes of paraneoplastic hypercalcemia in the species. 35 Metastasis to the iliosacral lymph nodes is detected before distant spread to lungs, liver, and spleen, and the metastatic rate reaches 50% to 90% by the time of diagnosis. 57 Staging requires 3-view thoracic radiographs, abdominal ultrasound with or without abdominal and thoracic CT, and ionized calcium measurement. 1 CT is the gold standard for primary tumor size measurement and is more accurate than ultrasonography for identifying abnormal lymph nodes. 6 Altered ultrasonographic appearance of lymph nodes is highly consistent with metastatic disease on cytology and histopathology. 9 Closed anal sacculectomy is the recommended surgical technique for AGASACA, as it keeps the anal sac intact, reducing contamination of surrounding tissue and the risk of postoperative infection; the open technique is considered inappropriate for neoplastic anal sacs. 7 A modified closed technique facilitating full anal sac duct excision has been described and is well tolerated, with no intraoperative complications and only one minor postoperative complication (paraparesis, which resolved) reported. 12 Perineal surgery carries a minor complication rate of approximately 12%, with an additional 12% of cases requiring further surgical intervention. 9 Lymphadenectomy for locoregional iliosacral lymph node metastasis is a recommended adjunct to primary tumor excision, with lymph node metastasectomy carrying low morbidity — minor controllable intraoperative bleeding was the only complication in 5% of metastasectomy procedur